Abstract While the prevalence of childhood obesity may have started to plateau for some groups of children,1-5 other groups such as low-income and minority children are experiencing increases in childhood obesity.4,5 These growing disparities may be linked to unanswered questions regarding the home environment and childhood obesity. For example, research has shown that healthful food availability/accessibility in the home, frequent family meals, and authoritative parenting style are associated with healthful dietary intake,6-8 better psychosocial health,9 and fewer unhealthy weight control behaviors10-13 in youth, but findings are inconsistent across studies with minority and low-income families.14,11,15,16 These conflicting findings suggest that mixed- methods studies are needed for an in-depth examination of the home environments of diverse families to identify potential explanatory mechanisms of childhood obesity that may have been overlooked in prior research. In addition, previous studies have not included state-of-the-art measures that may help illuminate factors in the home environment that differ by race/ethnicity. The primary objective of this study is to identify how familial factors, including interpersonal relationships that exist between family members, of racially/ethnically and socioeconomically diverse children act as risk or protective factors for predicting childhood obesity. To achieve this objective, a two-phased incremental mixed-methods approach will be used. Phase I (yrs. 1-2) will include in-home observations of diverse families (n=120; 20 each of African American, American Indian, Hispanic, Hmong, Somali and white families) to identify individual, dyadic (i.e., parent/child; siblings), and familial factors that are associated with, or moderate associations with, childhood obesity. The in-home observations, using our community-based participatory research partners, will include: (1) an interactive observational family task and family interview; (2) ecological momentary assessment (EMA)17 of parent stress, mood and parenting practices; and (3) child accelerometry and 24-hour dietary recalls. Using state-of-the-art measures, such as EMA, will allow for identifying within-day fluctuations in parenting practices or parent stress levels, which may help to identify nuances within the home environment that amplify or exacerbate childhood obesity risk. Results from the in-home observations will be used for rich analyses and to inform the development of a culturally-appropriate survey in Phase II (yrs. 3- 5). The survey will be administered at two time points to a diverse sample of up to two caregivers (n=2400) of children ages 5-7. Individual, dyadic, and familial factors that are longitudinally associated with child BMIz score and weight-related behaviors will be identified. Phase I and II recruitment will occur via the electronic Primary Care Research Network in Minnesota primary care clinics (n=82). This comprehensive evaluation of diverse home environments will identify potential factors that increase childhood obesity risk in order to create culturally-tailored interventions that will be effective in reducing childhood obesity disparities.